For many years, a small number of companies have sold vehicle crash barriers primarily designed to thwart deliberate vehicle-based attacks of buildings. These barriers are generally heavy steel structures imbedded in concrete or concrete structures in a road surface that physically obstruct the roadway. These heavy steel structure devices are designed so that a barrier device (usually a steel plate) can be raised or lowered to control the ability of a vehicle to pass through or over the barrier and, thus, gain access to the building being secured. These devices differ from the barriers commonly encountered in parking garages and other public venues, in that they have very high stopping power, for example, preventing a 15,000-pound explosive laden truck traveling at 50 mph from passing beyond the vehicle barrier.
Barriers come in numerous designs, but they can generally be categorized in three conventional types: plate, beam, and bollard. The plate barrier can be oriented to lay relatively flat on the surface of the roadway and be selectively actuated to be angled upwardly upon a perceived threat to form a wedge that restricts passage of a vehicle. The plate barrier is considered to be a permanently installed device as the plate is supported on a concrete encased frame that is buried into the surface of the roadway. A variation of the plate barrier has been introduced recently into the marketplace as a portable barrier. Another variation is to fasten the plate barrier to the roadway, such as with bolts. This barrier device is essentially a plate type barrier that is not imbedded in concrete, but instead can be moved to different locations to accommodate the need for temporary or changing security needs. Since the portable plate barrier is not imbedded in concrete, stopping power is relatively limited.
The beam barrier incorporates a vertically movable beam that is typically pivotally supported at one end of the beam by a steel support that is imbedded in concrete to provide a relatively immovable object and at the opposing end by a similar steel support at the opposing side of the roadway. The beam barrier serves as a movable gate that can be raised vertically (or swung horizontally) to allow vehicles to pass or lowered into engagement with the steel supports at either end of the beam to provide a substantial resistance to the passage of any vehicle. As with the conventional plate barrier, the beam barrier provides a permanent installation and relatively high stopping power. Some beam barriers use bands of nylon or similar material that are contained within the hollow beam and wrapped around the pivot structure for the beam to increase the resistance of the steel beam.
The bollards are typically permanently installed steel or concrete barriers that are typically not selectively movable, although vertical movement could be provided to permit the structure to rise into a passage restrictive position above the surface of the roadway, or be retracted into the ground to permit the passage of vehicles. Generally, bollards are a permanent structure that cannot be made portable without loss of substantial stopping power capabilities.
Conventional barriers generally have a disadvantage inherent in their designs in that each barrier design requires active mechanical movement of very heavy structures. Heavy steel plates (plate barriers) or heavy cylinders (bollard barriers) have to be raised against gravity in order to stop vehicles. Further, current vehicle barriers require approximately two seconds for emergency activation from an open position in which the vehicle can pass by the barrier to a deployed position in which a vehicle is prevented from passing by or over the barrier. Activation times for conventional beam barriers and sliding gate barriers are even longer, averaging about ten seconds for barriers that are one traffic lane wide and substantially longer for larger two lane barriers.
A vehicle traveling 50 mph covers 73 feet per second. Even if the barrier activation time is only two seconds, the facility needs to have almost 150 feet of standoff distance between the barrier close signal, such as from a guard or automated system, and the physical location of the barrier itself. Many facilities simply do not have the necessary space to accommodate this type of operation. This means that many existing barriers are seldom used in an “activate only when needed” mode. Thus, the barrier is always up and must be lowered for every authorized vehicle.
In addition, this constant raising and lowering of the vehicle barrier to allow authorized vehicle passage, over the course of its operating lifetime, requires a vehicle barrier to be cycled open and closed hundreds of thousands or even millions of times. Requiring constant movement from highly massive structures presents substantial challenges with respect to the maintenance and repair of vehicle barriers. Simply reducing the weight of the vehicle barrier is not a satisfactory resolution to these maintenance challenges as the stopping power of the vehicle barrier must be maintained.
With regards to the prevention of terrorist attack in ever-changing locations, such as roadblocks or military field installations, conventional barrier systems are generally impractical, as they require extensive installation procedures. In addition, such conventional barrier systems are often unable to stop a large terrorist vehicle, such as a 25,000-pound explosive laden trash truck, as has been employed in Lebanon, in a sufficient distance to prevent tremendous damage to the terrorist's intended target.
In view of the above mentioned disadvantages of conventional vehicle barrier systems, it is an object of the present invention to provide an improved vehicle restraint system that is highly portable, manufacturable at a lower cost than conventional systems, easily controllable, requires a low level of maintenance, yet is a highly effective barrier for security purposes.